Radio receiving apparatus



Dec. 5, 1933. A. H. GREBE RADIO RECEIVING APPARATUS Filed June 3, 1931Patented Dec. 5, 1933 UNITED RADIO' RECEIvING'APP'ARATIjs i e r emmsnmApplicfiiqn 1 3 Serial 541,929

7 Claims. 01.178 41) and by a definite amount, at the wish of the) r v Icoils L1 and L2 are ordinarily fixed in'theamount" operator.

Several. circuit arrangements suitable 'for' 10 carrying my inventioninto effect, are illustrated in the accompanying drawings, but Iido notwish to be understood asintending tolimit myself to the exact detailsshown,'as various changes'may be made therein within the meaning of thej'present invention, asset forth in the appended claims.

In .the drawing, Figure .1. shows the normal assembly of asuperheterodyne receiver; Figure 2 shows a circuit. detail of one stageof the intermediate frequency amplifier, Figure 3 shows.

a circuit detail-of part of the intermediate frequency amplifierequipped with my resonance changing arrangement. Figure 4 shows thedifference selectivity characteristics of the circuit,

3; Figure 6 shows a further modificationof my tuning" arrangement.

Referringjto Figure 1, A-is the tuned input cir'cuitof thesuperheterodyne receiver and B isthe local oscillator. 'The combinedaction of the local oscillator B and the tuned receivingcircuit A is toproduce a signal modulatedwave having a frequency much lower than thatof the v incoming signal. "This lowered frequency (calledtheintermediate frequency) is supplied to the intermediate frequencyamplifier C, (hereafter From the amplifier, the signal ordinarily issupplied to an audio fre-" 40. quency amplifier D and thence vto theloud abbreviated I F A).

speaker E.

Myinvention has to do specifically with an it will be understood that myinvention does" not [require any specific type of tube as it func- Vtions equally well whatever type of amplifying tube'may be used. 7 A

as obtainable with my invention. Figure 5 shows. a-possible modificationof the scheme of Figurethe"selectivity'curves ofthe IF A stage signal tog'et thespecified'output. r

Theinput circuitof tu'be T1 and the input'cir-' cuit 'of tube T: areboth normally of 'thetuned type and theyare so shown in'Fig. 2. Thevalues of L1C1",' and LzC2 are chosento giveresonance atthat'fre'q'uency chosen for the intermediate frequency; I'have'supposedit to be 175 -kilo-- cycles, a valueordinarily used today'.; The twooftheir inductance, and -in -'the degreefiof their I magnetic coupling and'I have so shown them in' ggq Fig. 2. The condenser Ci and C areordinarily of the adjustable type so that when the set is; assembled inthe factory the two circuits' ;L1"--C1 and -L2-C2 can be properly tuned.These two;

circuits are generally adjustedonceio'r all fat o."

the factory, when the set is built. 7 y In- Fig.3 I haveshown a circuitdetail of the I F A; (the amount shown inside the dotted rectangle ofFig. -"2) with my 'fimproved circuit arrangement attached? Inserieswit'h" each of 75 the'two circuit's Li -Grand Lz -Cz I have added:

a condenser';"Ca and; 015 respectively.' These addedcondenser's aresuitably of a-capa'citj much greater than-tlie capacity of condenser 01and:-

C2. These twocondensers {Cg and 'Cb have-their 0 terminals brought tothe connections of "atwo way switch S so arranged that when; thrown intoone direction-C s i's-shortcircuitedand when' thrown in the otherdirecti'on'condenser Cb' is" short circuited; f 5 5 "The i change in"circuit selectivity" for the ewe positions of the switch, when thecircuit hasbeen adjusted for- '-proper "performance; is shoWn by theresponse curves" of Fig.4, -I-Iere areshow i 3, for the two positionsofswitch-S. i 5

As will be explained later one positionj'of the switch S result's'in thetwo circuits being tuned" to each other; for this'position' the response5; F curveof the I FAstage'isl shown'by' the solid95 .line'curve A, ofFig. 4. "Itis supposed that the frequency for'which'the I FA hase beenbuilt is kilocycles '(175 kc), and curveA shows that thisfrequencyirequires-the minimumimpressed Thus it may beseen that'itrequires -l00 micro-voltsinput'togive the specified output at either 170kc or kc, but it requires onlyabout 2 micro -volts at'1'7 -5'-kc.' At'either "l60"-kc or 190 kc, the required input voltage isiaboutsbojomicro s V4 v ow. such aselectivitycurve'tends greatly to eliminateinterference" between" two stations-1 transmitting on nearly thesamefrequericy andit-- v is because of tlie'use of tund intermediaterig- 116" to bringthis about; curve B shows substantially frequencyof,17 5 kc per second.

quency amplifiers of this kind that the superheterodyne receiver hasbecome known as a high- 1y selective receiver.

Such high selectivity is however not always desirable, because of thecircuits discrimination against the higher frequency audio tones carriedby the modulated high frequency wave. It is many times desirable todiminish the sharpness of the resonance curve provided that gain infidelity of reproduction of the audiofrequency signal can be obtained.Many makeshift schemes have been advocated to carry out this task butthey have involved great loss in sensitivity of the receiver ordifficulty in manufactur ment of the set. I I have found it possible tochangethe formof the selectivity curve from that of curve A of Fig. 4 tothat of curve B of the same figure.

Furthermore, I have found it'possible to bring about the change in formof the selectivity curve e anda justr without appreciably sacrificingthe sensitivity of 6000 cycles'ofthe carrier frequency. It can be seenfrom curve B of Fig. 4 that I have been able the. same amplificationforall frequencies between-1'10 kc andl kc per second. As stated before,the I F A has been designed for a resonant Referring again to Fig. 3, Iwill explain condensers C1 andpa in series. This means, of

course, that the capacity of C2 is adjusted to a value-:slightly les'sthan thatof 01 The exact difference between the capacity of C1 and C de"pends upon the ratio of the capacity .of'cona For thepurpose'of myinvention, C1 may have a capacity 7 denser Ca to that ofthecondenserCnabout 6% that of C2. I do not limitmyself to such-a proportion howeverbecause it may be ad-. visable to use-a larger or smaller proportionthan 1 this under special conditions. I 7

The coupling between coils L1 and L2 must be suitably chosen if aselectivity curve such as that of curve A, Fig. 4, is tobe obtained. Iam assum ing that such a value of coupling hasbeen chosen.

Thecapacity of Chis about the same as the capacity of Ca,.when C1 and C2are of approximatelythe' same capacity. In case C1 andC2 are notapproximately the same, then the capacity of Cb will not be the sameasthat of. Ca; It will'be understood, of cours,e,.that when C1 is notequal to C2, the values of inductances, L2and L1 will correspondinglydiffer.

;I- Iay-ing now adjusted theset, with switch S in contact, asabovedescribed, the selectivitycurve will beabout as, shown by curve Aof Fig. 4.

Bynow shifting theswitch S to position 2, the

selectivity curve changes inform to that of curve B- 1of"Fig., 4. Thischange in formof curve is broug t about by e de-tu i s o th rcuitparatus.

how thedesired result is obtained. In tuning'up, or -adjusting the I F Ain the factory, the switch Sis thrown to position 11'. This shortcircuits 40.-condenser Ca-The two condensers C1 and C2, which are of theadjusta-bletypegare now regu latedfor capacity to bring about tuning ofthetwo circuits. Ifthe two coils L1 and L2 have the Y same inductance,this tuningoperation involves the equilization of the capacityof C tothat of in fidelity is accomplished with practically no loss insensitivity.

Whereas I have shown the switch S'as' short circuiting a condenser, inone circuit or the other, it is quite possible to short circuit a smallinductance instead. This possibility is indicated in the arrangement ofFig. 5, in which the two positions of switch 3 short circuit either coilLa or coil Lb. These coils-would normally have an inductance about 6%that of L1 or L2 its exact value, however, may depart appreciably fromthis value. i "i In Fig. 6, I have showna scheme in whichfthe" switch Sin the closed position shortcircuits condenser Cb in one circuit andinductance. Lain theother circuit and inthefopen? position removes theshort circuit fromIboth pieces of ;ap.-*

The two circuits are tuned, with the. switch in either position, and theresultant se'-' lectivity is thatgof curve A,.Fig'. .4; Thenwhen theswitch is thrown into its otherposition, the natural-frequency of onecircuit is raisedand that of the other is lowered. This condition;results-in the selectivity curve shown at B of Fig. 4. Y

Having thus described my-invention, what I1 claim is:

1". In combination witha pair of loosely coupled tuned circuits, meansincluding? auxiliary .reactances for increasing the'natural frequency ofone s circuit by a small :amount and decreasingv :the natural frequencyof thelother, circuit by approX-' I imately the same amount.

2. In a superheterodyne receiver having .an in'-' termediatefrequencyamplifier using two coupled,-

tuned circuits between successive vacuum tubes, i:

means for changing the shapeof'the, selectivity: curve, the said-meansincludingauxiliaryreacev tances for detuning the two tunedcircuits byincreasingthe natural frequency of one of the circuits by a small amountand decreasing thena *turalfrequency Ofthe other.circuit; ,by approxiimately the same amount as the first one lias been increased, V 3. In asuperheterodyne receiver having; an intermediate frequency amplifierusing .two coupled tuned circuits between successive vacuum tubes, meansfor successively increasing the natural fre-,: quency of one of thecircuits by a small-amount andthen decreasing the natural frequencyofthe other circuit by the same amount; 1

4. In the intermediate frequency amplifier of".

a. superheterodyne receiver, utilizing coupled tuned circuits forinterstag'e coupling, a switch ing arrangement for successivelyincreasing the capacitive reactance of one of the tuned circuits by asmall amount and thendecreasing the ca pacitive reactance of theoth ertuned circuitby';

approximately the same amount.

5. In a superheterody ne receiver having a tuned intermediate frequencyamplifier, said amplifier'utilizing magnetically :coupled, tunedcircuits between successive amplifying tubes, said tuned circuits eachhavinga coil and two 0on densers connectedin series-switching, meansfor:

successively removing a short circuit fromla conintermediate frequencyamplifier, said amplifier, 1

switch for increasing the natural frequency of one of the circuits by agiven amount, and de creasing the natural frequency of the other circuitby approximately the same amount.

'7. In a superheterodyne receiver having a tuned using coupled tunablecircuits, a single control switching arrangement which servespractically to instantaneously change the electrical characteristics ofthey two circuits so that the tuned frequency of one circuitis increasedby a given amount and the tuned frequency of the other circuit islowered by approximately the same amount. v

. ALFRED H. GREBE.

DISCLAIMER 1,937,564.Alfred H. G'rebe, Hollis, N. Y. RADIO RECEIVINGAPPARATUS. Patent dated December 5, 1983. Disclaimer filed April 14,1936, by the assignee, Radio Corporation of America. Hereby entersdisclaimer to claims 1, 6, and 7 of said Letters Patent.

[Ofiicial Gazette May 12, 1936.]

